Early detection of disease states in mammals has been the focus of much recent research. For disease detection, the public-health community has historically relied on laboratory tests that can sometimes take days or even weeks to return a result. The increased availability of better and faster diagnostic tests, however, promises the possibility of more automated and earlier disease detection and subsequent intervention. It is believed that introduction of therapy early in the disease process will reduce the mortality rate associated with the disease and shorten the time for treatment.
Acute renal failure (ARF) secondary to renal injury, including but not limited to ischemic injury and nephrotoxic injury, remains a common and potentially devastating problem in clinical nephrology. Five percent (5%) of hospital admissions and 30% of Intensive Care Unit admissions have acute renal failure, and 2-5% of hospitalized patients will develop it. Acute renal dysfunction occurs in up to 40% of adults following cardiac surgery. Pathophysiologic mechanisms include diminished renal blood flow, loss of pulsatile flow, hypothermia, atheroembolism, and a generalized inflammatory response. ARF requiring dialysis also complicates up to 10% of cardiac surgeries in infants and children with congenital heart disease.
ARF persistently continues to result in a high rate of mortality despite significant advances in supportive care. Pioneering studies over several decades have illuminated the roles of persistent vasoconstriction, tubular obstruction, cellular structural and metabolic alterations, and the inflammatory response in the pathogenesis of ARF. While these studies have paved the way for successful therapeutic approaches in animal models, translational research efforts in humans have yielded disappointing results, for reasons such as the multifaceted response of the kidney to ischemic injury and a paucity of early markers for ARF with a resultant delay in initiating therapy.
Animal studies have shown that, while ARF due to ischemia can be prevented and/or treated by several maneuvers, treatment for ARF must be instituted very early after the ischemic insult. A major reason for the inability to provide preventive and therapeutic measures for ARF in humans is the lack of early biomarkers for ARF. Thus, the identification of a reliable, early biomarker for impaired renal status would be useful to facilitate early therapeutic intervention, and help guide pharmaceutical development by providing an early indicator of nephrotoxicity.
The traditional laboratory approach for detection of renal disease involves determining the serum creatinine, blood urea nitrogen, creatinine clearance, urinary electrolytes, microscopic examination of the urine sediment, and radiological studies. These indicators are not only insensitive and nonspecific, but also do not allow for early detection of the disease. In current clinical practice, ARF is typically diagnosed by measuring a rise in serum creatinine over time, which is an unreliable indicator for measuring acute changes in kidney function. Indeed, while a rise in serum creatinine is widely considered as the “gold standard” for the detection of ARF, it is a late indicator of renal injury since as much as 50% of the kidney function may already be lost by the time the serum creatinine changes.
The lack of early biomarkers for acute renal injury thus has severely slowed progress in finding effective therapies within the narrow window of opportunity. The identification of urinary protein biomarkers suitable for the early detection and diagnosis of acute renal injury holds great promise to improve the clinical outcome of patients. It is especially important for patients presenting with vague or no symptoms or with acute renal injury following surgery such as cardiopulmonary bypass surgery.
Although efforts to evaluate disease processes and drug effects have traditionally focused on genomics, more attention has been paid recently to proteomics due to its offering a more direct, complete and promising understanding of the biological functions of a cell. The term “proteomics” was coined to make an analogy with genomics, and while it is often viewed as a continuation of genomics, proteomics is much more complicated than genomics. Most importantly, whilst the genome is a rather constant entity, the proteome differs from cell to cell and is constantly changing through its biochemical interactions with the genome and the environment. One organism will have radically different protein expression in different parts of its body, in different stages of its life cycle and in different environmental conditions.
The protein map of a biological system, including a cell, sub-cellular fraction or expression media, can be referred to as a proteome. Proteomics, or analysis of the proteome of a biological system, offers a relatively new approach to protein expression profiling and cellular or tissue protein identification from samples that are obtained under various specified conditions. Proteomics has an enormous breadth of application ranging from investigation and identification of biomarkers, molecules that are indicative of a particular pathological state, which in turn can be used for diagnostic purposes and targets for therapeutic intervention. Proteome analysis allows the investigator to obtain information on protein identity, protein-protein interaction, the level of protein expression and protein expression profiling, protein trafficking and turnover, protein variants, and protein post-translational modifications.
Traditionally, proteomics combines two-dimensional electrophoresis (2-DE), a high-resolution protein separation technique, with mass spectrometry (MS). Proteomics research is targeted towards characterization of the proteins encoded by a particular genome and its changes under the influence of biological stimulation. Proteomics also involves the study of non-genome encoded events such as the post-translation modification of proteins, interactions between proteins, and the location of proteins within the cell. The study of gene expression at the protein level is important because many of the most important cellular activities are directly regulated by proteins in the cell rather than by gene activity. Also, the protein content of a cell is highly relevant to drug discovery and drug development efforts since most drugs are designed to target proteins. Therefore, the information gained from proteomics is expected to greatly boost the number of drug targets.
Neutrophil gelatinase-associated lipocalin (NGAL) has recently been identified as an early and immediate biomarker of impaired renal status, which has been disclosed in U.S. Patent Application Publications US2004/0219603, US2005/0272101, US2005/0261191, and US2007/0037232, which are incorporated herein by reference.
Nevertheless, there remains a need to identify other reliable biomarkers for the early determination of renal injury and disease caused by ischemia and/or nephrotoxicity. It would also be advantageous to provide testing of a mammalian subject's urine, blood serum, or other body fluid samples for early biomarkers of acute renal injury within minutes or hours of a suspected injury, since early biomarkers for acute renal failure may begin to appear at low levels and continue to rise thereafter. It would likewise be advantageous if early biomarkers for acute renal injury could be detected in bodily fluid samples such as blood serum and urine shortly after the onset of a renal event that could lead to renal tubular cell injury. There is also a need to provide reliable and accurate methods of early determination of the existence of acute renal injury in patients, the results of which can then be used to manage the treatment of affected patients.